The present invention relates generally to the field of voice recognition and more specifically to a system and methodology for verifying a speaker by comparing a selected utterance of the speaker against a previously recorded selected utterance by the same speaker utilizing computed moment invariants of the selected utterance for comparison purposes.
The transaction of authorizing advances of money, transfer of funds, and the granting of credit, along with other associated business transactions, have reached the point where a credit card or other form of indicia, carrying magnetically encoded information, is used by a customer to activate an unattended business machine, for example, a teller terminal. A number of safeguards have been built into these systems to insure that the customer is indeed the rightful owner of the card and as such has the authorized use of the business machine. One type of system in present use is activated by a magnetically encoded credit card and verification is accomplished by having the customer key into the terminal a secret number which number was assigned to the customer at the time the card was issued. The business system compares the secret number entered by the customer against a corresponding number that is encoded on the card itself or stored in a central computer location. A correspondence in number entered and number recorded permits the customer to have access to the machine.
Another prior art system utilizes a fingerprint comparison by having the customer position his finger or hand over a scanner which in turn causes the scanner to generate signals indicative of certain key features of the customer's fingerprint, which key features are checked against recorded key features on a customer's credit, or access card.
A particularly interesting type of system is one wherein the customer's voice is used to provide the verification of his identity. Prior art systems that operate by having the customer speak a verification phrase for comparison against a prior recorded reference phrase have been developed. The reference phrase may be recorded on a credit card or within the system.
A number of techniques have been developed in order to ascertain the reliability of the verification. A typical voice recognition system is described in U.S. Pat. No. 3,509,280 entitled "Adaptive Speech Pattern Recognition System", by J. W. Jones, and in U.S. Pat. No. 3,649,765 entitled "Speech Analyzer-Synthesizer System Employing Improved Format Extractor", by L. R. Rabiner et al.; and in U.S. Pat. No. 3,700,815 entitled "Automatic Speaker Verification By Non-Linear Time Alignment Of Acoustic Parameters", by G. R. Doddington et al. Additional systems are disclosed in U.S. Pat. No. 3,812,291 entitled "Signal Pattern Encoder And Classifier" Brodes et al. and in U.S. Pat. No. 3,816,722 entitled "Computer For Calculating The Similarity Between Patterns And Pattern Recognition Systems Comprising The Similarity Computer", by Sakoe et al. Some publications of interest for showing the state of the art are "Experimental Studies In Speaker Verification, Using An Adaptive Sytem", by K. P. Li et al.; Journal of the Acoustical Society of America Vol. 40, No. 5, 1966, pp. 966-978; "Automatic Speaker Verification Using Cepstral Measurements", by J. E. Luck, Journal of the Acoustical Society of America, Vol. 46, No. 4 (part 2) 1969, pp. 1026-1029; "Pattern Matching Procedure For Automatic Talker Recognition", by S. Pruzansky, Journal of Acoustical Society of America, Vol. 35, No. 3, pp. 354-358; and "Visual Pattern Recognition By Moment Invariants", by Ming-Kuei Hu, IRE Transactions On Information Theory, 1962, pp. 179-187.
The last named article establishes a theorem which is useful for visual pattern recognition of geometrical patterns and alphabetical characters, independently of position, size and orientation. The present invention utilizes select modifications of this theorem to implement a system for recognizing and verifying the standardized utterance of a cooperative speaker.